Not Applicable
Not Applicable
This invention relates to methods of and devices for generating magnetic fields, and more particularly to the physical characteristics of magnetic field generating coils.
There are various known methods for determining the position of a medical instrument during surgery. For instance, U.S. Pat. No. 5,592,939 to Martinelli, hereby incorporated by reference, discloses a method and apparatus for detecting the position of a medical instrument during surgery. This invention, however, is not limited to any specific method of determining the position of a medical instrument during surgery. For example, FIG. 1 is a diagram of an examination deck 200 with a medical instrument in a surgical environment. During surgery, for example, examination deck 200 lies below a patient. The medical device, such as a catheter 203, is placed inside the patient. Catheter 203 has a coil 14 at its distal end. Methods and systems consistent with the ""939 patent determine the location and orientation of catheter 203 inside the patient relative to examination deck 200.
Catheter 203 includes a conductor 16 that leads along catheter 203 to a location outside the patient. Examination deck 200 comprises magnetic field generating coils that produce magnetic fields within a navigational domain 12. The magnetic fields induce voltage signals in sensing coil 14. Measurements taken at conductor 16 of the induced voltage signals provide sufficient information to compute the orientation and position of sensing coil 14.
FIGS. 2A, 2B, 2C, and 3 show magnetic field generating coils. FIG. 2A is a diagram of a coil set 202 for generating a substantially uniform magnetic field in the X direction. Driver 28 supplies current in the direction indicated by the arrows. Coil elements 20 and 22 are horizontal, while coil elements 24 and 26 are vertical. Elements 24 and 26 are xe2x80x9ccompensationxe2x80x9d coils, i.e. xe2x80x9cCunardxe2x80x9d coils, which cancel some undesirable field components generated by elements 20 and 22 in the Y and Z directions. As a result, coil set 202 generates a substantially uniform X direction field as indicated by field line 27.
FIG. 2B is a diagram of a coil set 204 for generating a substantially uniform magnetic field in the Y direction. Coil set 204 includes element 30 spaced from element 32, but parallel to element 32. Driver 34 supplies current in the direction indicated by the arrows. Coil set 204 generates a substantially uniform Y direction field as indicated by field line 33.
FIG. 2C is a diagram of a coil set 206 for generating a substantially uniform magnetic field in the Z direction. Driver 44 supplies current in the direction indicated by the arrows. Coil elements 36 and 38 are horizontal, while elements 40 and 42 are vertical. Elements 40 and 42 are compensation coils, i.e. Cunard coils, that cancel some undesirable field components in the X and Y directions. As a result, coil set 206 generates a substantially uniform Z direction magnetic field as indicated by field line 43.
FIG. 3 is a diagram of three pairs of delta coil sets 300 for generating three gradient magnetic fields. The configuration includes a first delta coil pair 50-52, a second delta coil pair 54-56, and a third delta coil pair 58-60. Delta coil pairs 50-52, 54-56, and 58-60 are arranged in a circular orientation about the Y axis such that there is an axis perpendicular to the direction of elongation of the coils at , 120 , and 240 relative to the Z axis. The magnetic field generated by long delta coil 50 and short delta coil 52 is shown by the field lines extending from coils 50-52. The field lines from delta coils 50-52 group form a family of substantially constant signal surfaces, i.e. the magnetic fields have a spatial gradient in two of the axis dimensions and a substantially zero field value in the remaining axial dimension.
Discussion of FIGS. 1, 2A, 2B, 2C, and 3 are for illustrative purposes only. See U.S. Pat. No. 5,592,939 for further examples.
FIG. 3B is a diagram of a patient undergoing cranial surgery with a device consistent with this invention. In FIG. 3B, the medical device is a probe 302 that is placed inside a head 308 of a patient.
Coil sets 202-204, 300 in FIGS. 2A-2C, and 3 are contained within the examination deck 200 of FIG. 1. Placing all these coils in examination deck 200, however, causes examination deck 200 to be relatively thick. It is desirable, however, that examination deck 200 be relatively thin for a number of reasons. First, a thinner examination deck 200 is lighter, less cumbersome, and requires less space in a crowded surgery room. Second, if coil sets 202-204, 300 are arranged so that each is a different distance from navigational domain 12, then the magnetic field strength in navigational domain 12 from each coil set is different. Different magnetic field strengths reduce accuracy of the positioning system. Further, it can be less expensive and easier to manufacturer a thin examination deck as compared to a thick examination deck.
Examination deck 200, in turn, is placed on an examination table 306. FIG. 3A is a diagram of examination deck 200 placed on the examination fable 306, consistent with this invention, in a medical setting. Examination table 306 introduces other design constraints,including the width and length of the examination deck 200, which introduces design constrains on the size and shape of coils inside examination deck 200. Preferably, the magnetic field generating coils are such that examination deck easily fits onto standard size examination tables, such as examination table 306.
Therefore, it is desirable to provide an apparatus that allows coil sets to be arranged substantially coplanar with respect to navigational domain 12. It is also desirable to provide an apparatus that allows examination deck 200 to fit on a standard examination table.
It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art.
The foregoing and other objects are achieved by the invention which in one aspect comprises an apparatus for determining a location of a sensor in a surgical navigation domain. The apparatus includes a first magnetic field generator having a first coil set, a second magnetic field generator having a second coil set. The first and second coil sets are disposed substantially within a common plane. The apparatus further includes a processor configured to receive a plurality of signals. The processor calculates the location of the sensor from the plurality of signals. The sensor produces the plurality of signals in response to magnetic fields generated by the first and second magnetic field generators.
In another embodiment of the invention, the first coil set includes at least one delta coil pair for generating a gradient magnetic field-in the navigation domain.
In another embodiment of the invention, each delta coil pair further includes one or more end correction coils. Each delta coil pair is electrically coupled to the corresponding end correction coil, and current flows through the end correction coil in a direction opposite of the direction of the current flowing through the corresponding delta coil pair.
In another embodiment of the invention, the second coil set includes at least one uniform coil pair for generating a uniform magnetic field in the navigational domain.
In another embodiment of the invention, the first coil set includes a first delta coil pair longitudinally oriented along a first axis, a second delta coil pair longitudinally oriented along a second axis, and a third delta coil pair longitudinally oriented along a third axis. The three delta coil pairs are arranged such that the second axis is rotated within the common plane substantially sixty degrees with respect to the first axis, and the third axis is rotated within the common plane substantially one hundred and twenty degrees with respect to the first axis.
In another embodiment of the invention, each of the first, second arid third delta coil pairs lies within a distinct plane that is parallel to the common plane, such that the delta coil pairs overlap one another.
In another embodiment of the invention, each of the first, second and third delta coil pairs includes two or more distinct coil elements, electrically coupled, such that the aggregate of the distinct coil elements produces the corresponding gradient magnetic field.
In another embodiment of the invention, intersecting delta coil pairs share one or more common coil elements.
In another embodiment of the invention, intersecting delta coil pairs include distinct coil elements in an intersecting region where the delta coil pairs overlap.
In another embodiment of the invention, each of the delta coil pairs further include one or more end correction coils. Each of the delta coil pairs is electrically coupled to the corresponding end correction coil, and electrical current flows through the end correction coils in a direction opposite of the direction of the current flowing through the corresponding delta coil pair.
In another embodiment of the invention, at least one of the delta coil pairs is characterized by a length that is different from the length of the other delta coil pairs.
In another embodiment of the invention, each of the delta coil-pairs includes a short coil and a long coil. The short coil further includes a first end correction element and a second end correction element for reducing unwanted magnetic field components. Electrical current flows through the end correction coils in a direction opposite of the direction of the current flowing through the corresponding short coil. The long coil further includes a central compensating coil for reducing unwanted magnetic field components. Electrical current flows through the central compensating coil in a direction opposite of the direction of the current flowing through the corresponding long coil.
In another embodiment of the invention, one or more of the delta coil pairs overlap a coplanar uniform coil pair.
In another embodiment of the invention, each of the one or more overlapping delta coil pairs includes two or more distinct coil elements. The distinct coil elements are electrically coupled, such that the aggregate of the distinct coil elements produces the corresponding gradient magnetic field.
In another aspect, the invention comprises an apparatus for determining a location of a sensor in a surgical navigation domain. The apparatus includes a first magnetic field generator including at least one delta coil pair for generating a gradient magnetic field in said navigation domain. The at least one delta coil pair disposed within a first plane. The apparatus further includes a second magnetic field generator including at least one uniform coil pair for generating a uniform magnetic field in the navigational domain. The at least one uniform coil pair disposed within a second plane. The first plane is offset from the second plane by an offset angle calculated to reduce undesirable uniform field components. The apparatus also includes a processor, configured to receive a plurality of signals, for calculating the location of the sensor from the plurality of signals. The sensor produces the plurality of signals in response to magnetic, fields generated by the first and second magnetic field generators.
In another aspect, the invention comprises an apparatus for determining a location of a sensor in a surgical navigation domain, including a first magnetic field generator having a common coil, a second magnetic field generator also including the common coil, and a processor for calculating the location of the sensor. The sensor produces a plurality of signals in response to a first magnetic field generated by the first magnetic field generator, and in response to a second magnetic field of a different shape, with respect to the first magnetic field generated by the second magnetic field generator.
In yet another aspect, the invention comprises a method of determining a location of a sensor in a surgical navigation domain. The method includes generating a first magnetic field using a first magnetic field generator having a first coil set, and generating a second magnetic field using a second magnetic field generator having a second coil set. The first and second coils are disposed substantially within a common plane. The method further includes calculating the location of the sensor from a plurality of signals. The sensor produces the plurality of signals in response to magnetic fields generated by the first and second generated magnetic fields.
In another embodiment, the method further includes generating a gradient magnetic field in said navigation domain using at least one delta coil pair for generating.
In another embodiment, the method further includes generating a gradient magnetic field in said navigation domain using two or more distinct coil elements, electrically coupled, such that the aggregate of the distinct coil elements produces the corresponding gradient magnetic field.
In another embodiment, the method further includes generating a gradient magnetic field in said navigation domain using delta coil pairs having one or more end correction coils. Each of the delta coil pairs is electrically coupled to the corresponding end correction coil, and electrical current flows through the end correction coils in a direction opposite of the direction of the current flowing through the corresponding delta coil pair.
In another aspect, the invention comprises a method of determining a location of a sensor in a surgical navigation domain, including generating a gradient magnetic field in said navigation domain using a first magnetic field generator including at least one delta coil pair disposed within a first plane. The method further includes generating a uniform magnetic field in the navigational domain using a second magnetic field generator including at least one uniform coil pair. The at least one uniform coil pair is disposed within a second plane. The first plane is offset from the second plane by an offset angle calculated to reduce undesirable uniform field components. The method also includes calculating the location of the sensor from a plurality of signals. The sensor produces the plurality of signals in response to magnetic fields generated by the first and second generated magnetic field.
In another aspect, the invention comprises a method of determining a location of a sensor in a surgical navigation domain, including generating a first magnetic field using a magnetic field generator that includes a common coil. The method further includes generating a second magnetic field of a different shape than the first magnetic field, using a second magnetic field generator that includes the common coil. The method also includes calculating the location of the sensor from a plurality of signals. The sensor produces the plurality of signals in response to magnetic fields generated by the first and second magnetic field generators.